236 INSTINCT. Chap. VII. 



for their similarity by inheritance from a common 

 parent, and must therefore believe that they have 

 been acquired by independent acts of natural selection. 

 I will not here enter on these several cases, but will 

 confine myself to one special difficulty, which at first 

 appeared to me insuperable, and actually fatal to my 

 whole theory. I allude to the neuters or sterile females 

 in insect-communities : for these neuters often differ 

 widely in instinct and in structure from both the males 

 and fertile females, and yet, from being sterile, they 

 cannot propagate their kind. 



The subject well deserves to be discussed at great 

 length, but I will here take only a single case, that 

 of working or sterile ants. How the workers have 

 been rendered sterile is a difficulty ; but not much 

 greater than that of any other striking modification of 

 structure ; for it can be shown that some insects and 

 other articulate animals in a state of nature occasionally 

 become sterile ; and if such insects had been social, and 

 it had been profitable to the community that a number 

 should have been annually born capable of work, but in- 

 capable of procreation, I can see no very great difficulty 

 in this being effected by natural selection. But I must 

 pass over this preliminary difficulty. The great difficulty 

 lies in the working ants differing widely from both the 

 males and the fertile females in structure, as in the shape 

 of the thorax and in being destitute of wings and some- 

 times of eyes, and in instinct. As far as instinct alone 

 is concerned, the prodigious difference in this respect 

 between the workers and the perfect females, would 

 have been far better exemplified by the hive-bee. If a 

 working ant or other neuter insect had been an animal 

 in the ordinary state, I should have unhesitatingly 

 assumed that all its characters had been slowly acquired 

 through natural selection; namely, by an individual 



